Copper solders and copper alloy solders are hard solders which have been used for soldering purposes in the past. In addition to using solders which exclusively or essentially exclusively consist of copper, copper alloy solders have found acceptance in the industry which contain between about 40 to 60% by weight of copper, small amounts of silicon, for example, 0.2% by weight of silicon, with the remainder being zinc. In some instances, nickel is also contained in such prior art copper alloy solders.
For the purpose of preparing such solders, the metal or the alloy are melted and the molten material is cast in molds, whereafter, by means of customary forming measures, such as drawing, pressing, or rolling, the material is formed into wires, profiles or sheets. It is also possible to produce powders by means of grinding. Customary fluxing agents can also be added or incorporated by melting.
Copper and copper alloy solders, in dependence on their use, exhibit the capability to react with the steel, cast iron, hard metal and the like to be soldered under the formation of solid solutions and/or stoichiometrically defined compounds. Such solders are then usually designated as reaction solders. In the hard soldering of steel, cast iron and hard metals in general, such solders are used to a large extent and for economical and technical reasons in the manufacture of machine parts, apparatus, devices, tools and electromotors and the like. In using such reactive solders, it is common, particularly in the soldering of steel and hard metal, such as tungsten carbide-cobalt-alloys, wherein the cobalt binder may be partially replaced by other metals as, for example, nickel, to perform the soldering procedure at relatively high temperatures, for example, above 1100.degree. C. either in vacuum or under a protective gas atmosphere. The term "hard metals" as used herein is deemed to refer particularly to tungsten carbide-cobalt-alloys which, in most instances, contain small, weighed out contents of carbon and wherein the binder metal cobalt may be replaced by other metals as, for example, nickel. However, the term also refers to titanium and tantalum carbides which, in like manner, usually contain cobalt and the other metals as binding agents.
Experience has shown that in using such prior art solders, for example, for the soldering of steel with hard metal, the desired results are not fully achieved. It has thus been ascertained that, for example, dissolution phenomena occur along the grain boundary of the steel resulting in corresponding lowering of the static and, primarily, the dynamic strength. In particular, the toughness of the steel in this region is markedly reduced. In hard metal, by contrast, a brittleness of the marginal zone by diffusion, formation of intermetallic phases and the so-called Kirkendall effect under formation of a brittle zone have been observed. Moreover, in some instances, the formation of an .eta.-like layer, primarily in the soldering of steel with the hard metal has been observed as a consequence of a certain carbon deprivation on the hard metal side of the soldered structure. Primarily, in subjecting the soldered system to impact, these negative diffusion related phenomena have resulted in impermissibly poor results.